Considerable effort has been directed toward reducing vehicle aerodynamic drag by sealing or spanning the air gap between the bodies of articulated vehicles. Thus, the railroad, bus, and truck industries all have devoted considerable time and resources toward this end. Reducing aerodynamic drag has the effect of increasing vehicle efficiency, which is usually reflected in the form of better vehicle fuel mileage. Both the surface or skin gap between adjacent bodies of articulated vehicles and the volume gap between the bodies contribute to the overall vehicle drag.
While this problem has been addressed in connection with buses and railroad cars, the trucking industry is faced with the most difficult air drag problems because the relative articulation between the vehicle bodies is the greatest. Typically, for trucks the maximum required yaw, that is, articulation about a substantially vertical axis through the fifth wheel assembly, is between about 90 and 110 degrees in each direction measured from a longitudinal straight-ahead running alignment. The maximum required relative pitch about a horizontal pitch axis intersecting with the yaw axis, usually at the fifth wheel assembly, is between about 5 to about 7 degrees. Finally, truck tractor frames will undergo dynamic torsional rotation or helixing about a horizontal roll axis, which also typically is about 5 to 7 degrees in both directions.
One approach which has been the subject of numerous patents, but has not been widely adopted in the trucking industry is to attempt to span or seal the gap between vehicle bodies by fairings, panels, resilient bodies or the like. Thus, U.S. Pat. Nos. 4,611,847, 4,397,496, 4,343,506, 4,141,755, 4,036,519, 3,834,752, 3,711,146, 3,425,740, 2,101,793 and D238,161 all disclose articulated truck tractor-trailer assemblies having side and top structures which extend across the gap between the cab assembly and the trailer body to reduce the vehicle's aerodynamic drag.
A third compromise approach also has been employed, namely, a combination of gap spanning mechanical structures and air deflectors.
These prior art mechanical gap-spanning systems, however, tend to suffer from problems of reliability and operating inconvenience. Some must be moved or removed to permit full relative articulation of the vehicle bodies, while others often cannot reliably accommodate repeated articulation, particularly at large angles. Additionally, movable, inflatable and elastic panel systems, particularly if they require deployment controls, can add significantly to the cost of the tractor-trailer assembly and they can be difficult to retro-fit to existing vehicles. Such mechanical gap-spanning devices also often present problems when the trailer must be detached or separated from the tractor, which may be required several times a day in some applications.
Another basic drag reduction approach which has been widely used in the trucking industry is to employ various fairings or deflectors on the tractor cab assemblies and/or trailer bodies to attempt to deflect air efficiently across the gap between cab assemblies and trailer bodies. Thus, U.S. Pat. No. 4,021,069 to Hersh, U.S. Pat. No. 2,514,695 to Dempsey, U.S. Pat. No. 4,210,354 to Canning and U.S. Pat. No. 3,971,586 to Saunders are typical of trailer-mounted nose cone assemblies, and U.S. Pat. No. 4,245,862 to Buckley, and U.S. Pat. No. 4,904,015 to Haines and German Patent No. 25 50 726 are typical of cab mounted deflectors or fairings.
Fairings and deflectors seek to present a more aerodynamic front for the vehicle assembly and/or smooth the air flow over the gap between the articulated bodies. While in some instances these systems reduce the skin gap and/or volume gap between bodies, such gap reduction is incidental and often there is still a very substantial tractor-trailer gap. Thus, aerodynamic drag reduction across the air gap between adjacent articulated truck bodies is only partially achieved by fairings and deflectors.
U.S. Pat. Nos. 4,518,188 and 4,156,543 employ a combination of side panels which are used to span the gap along the sides of the tractor-trailer assemblies, while roof-mounted air deflector assemblies are used to reduce drag across the roof assembly. Such compromise systems have some of the disadvantages of both gap spanning and air deflection.
In the mass-transit industry, articulated buses are well known which have accordion-like gap-spanning sleeves. These sleeves, however, are primarily designed to prevent access to the space between the bus bodies. The buses tend to operate at relatively low speeds, at which drag is not a serious problem, and the accordion pleats do not provide an optimum gap-spanning surface for air flow.
Similarly, U.S. Pat. No. 2,193,155 to Antoine is directed to an articulated bus in which a special midbody virtual pivot assembly is used to provide a walk-through passageway between the articulated components of the bus. The Antoine apparatus is designed to solve the problem of providing a walk-through, not to solve the problem of drag reduction. In fact, the Antoine assembly includes a substantial skin and volume gap in the top surface between the articulated bodies, it cannot accommodate relative articulation through large angles, it has no provision for accommodating relative roll between the bus components, and the trailing body cannot be separated from the lead body.
In the railroad industry U.S. Pat. No. 387,382 to Weems is typical of a gap-spanning system as applied to trains. The problems associated with rail-mounted vehicles, however, are much less severe since the yaw articulation angles are relatively small, and the pitch and roll articulation angles are virtually nil as compared to those in the trucking industry.
Accordingly, it is an object of the present invention to provide an aerodynamic drag reduction apparatus and method suitable for use on trucks to significantly reduce the aerodynamic drag which results from the gap between articulated bodies of such vehicles.
It is another object of the present invention to provide a tractor-trailer drag reduction apparatus and method which does not rely upon a plurality of mechanical and/or moving parts to effect drag reduction.
It is still a further object of the present invention to provide a tractor-trailer drag reduction apparatus and method which enables utilization of a standard fifth wheel assembly of the type widely employed in the trucking industry.
Apparatus and method of the present invention have other objects and features of advantage which will become more apparent from, and are set forth in detail in, the following Best Mode of Carrying Out the Invention and the accompanying drawings.